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2021-04-15 13:31:59 -05:00
Magnetic stripe technology
Figures and listings are at the end.
Because of their widespread use, most magnetic cards adhere to well-defined
standards that describe the physical and magnetic characteristics for a
magnetic stripe on a plastic card. These standards outline specifications for a
storage format and information interchange. This does not preclude other
encoding techniques or additional data tracks for specific applications, but in
most cases it makes sense to adhere to at least the basic constraints. This
gives you the choice of using any commercially available magnetic encoders for
your application. The technique used for encoding magnetic cards is known as
"Two-Frequency, Coherent Phase Recording". Allowing for the representation of
single-channel, self-clocking serial data, this methodology is generally
referred to as F/2F. Self-clocking is achieved by combining data and clock bits
together in a continuous, synchronous sequence. In this scheme, an intermediate
flux transition signifies a one bit and the absence of an intermediate flux
transition denotes a zero bit.
Three data tracks defined for use on standard magnetic cards each possess
different bit densities and encoded character sets. The average bit density of
track 1 is 210 bits per inch (bpi). Track 1 characters are made up of six data
bits and an odd parity bit, encoded with the least-significant bit first and
the parity bit last, yielding a 64-character set. Taking the number of bits per
inch and the number of bits per character, you can see track 1 has the capacity
to hold 79 characters.
Track 2 has a bit density of 75 bpi, and track 3 uses 210 bpi. Both of these
tracks allow the representation of a numeric-only character set. The characters
for tracks 2 and 3 are encoded using a 4-bit binary-coded decimal subset with
odd parity and, like track 1, are encoded with the least significant bit first
and the parity bit last. The lower density of track 2 allows up to 40 numeric
characters, where 107 numerics can be squeezed onto track 3. The actual number
of usable characters will be fewer since you also have the Start Sentinel, End
Sentinel, and LRC characters.
Though sometimes magnetic cards are moved past the read head mechanically,
most applications rely on manually moving the card, either through a slotted
reader or into an insertion-type reader. Typically the swipe rate is 5-20 inches
per second (ips), with 50 ips being the fastest most card readers can handle. Of
course, moving the card by hand will not only result in varying the absolute
card velocity but, will also introduce incremental speed changes as the card
accelerates and decelerates past the pickup. The F/2F scheme is very forgiving
of such speed fluctuations.
For all 3 tracks, the fundamental data format is similar and consists of the
following elements: First, leading zero bits are encoded to indicate the
presence of an encoded magnetic card and provide synchronization pulses to the
read head electronics and ultimately to the controller. Next, the Start Sentinel
character is encoded which indicates the start of the actual data. The coded
data follows. Next, the End Sentinel terminates the data portion of the card
and followed by an LRC byte (used for error detection). The LRC is essentially
a horizontal parity calculated by an exclusive-OR of all the data bits from the
Start Sentinel to the End Sentinel (inclusive). Finally, trailing zeros follow
the LRC and fill out the remainder of the card.
ANATOMY OF A MAGNETIC CARD
The magnetic tracks have inherent characteristics based on details such as
code set and bit and character densities. International organizations such as
Mastercard and VISA impose additional constraits for their participating members
and standards exist for bank debit cards and ATM cards as well. These rules
specify the exact content and format of each data field in aech track as well as
the intended uses for the tracks. Naturally, for nonfinancial uses, it is not
necessary to comply with these standards. For dedicated uses such as access
control, people tracking, and material tracking, adhering to the minimal
standards is adequate.
The most-often-used track is track 2, although it offers the lowest inform-
ation density of the three. It contains all the information that is normally
used for credit card transactions. When a customer name is required, track 1
must be used since it is the only track that permits alphanumeric data. Track 3
is specified for numeric-only data, but is unique. It is intended for change-
able data and consequently may not only be read but may be rewritten by the
transaction-handling equipment. A multitude of data fileds are contained in
these various tracks. Figure 1 shows a brief run-down of what is generally
placed on tracks 1 and 2.
REAL CARD READERS
The recovery of magnetically encoded F/2F data can be accomplished directly
with the use of just about any microcontroller. There are no particular
difficulties in deciphering the raw F/2F data stream and many early magnetic
read heads contained nothing more than signal amplifiers and line drivers.
These are now artifacts since all modern magnetic read heads contain integ-
rated F/2F bit recovery circuitry and interface with the host controller in a
standard fashion using three wires: CARD PRESENT, CLOCK, and DATA. The read
heads usually rely on a single chip to perform the linear signal conditioning,
sychronization, and recovery of individual bits from the data stream. The Mag-
Tek 21006505 IC is representative of this type of data recovery circuit and its
functionality is depicted in figure 2.
Linear conditioning consists of raising the level of the magnetic pickup's
input signal, rejecting common-mode noise, conditioning and detecting the
signal, and finally providing a digital output for susequent processing. The
enable/disable counters provide initialization for the recovery section. The
recovery section locks onto the data rate and recovers the individual data bits
from the data stream. The oscillator section provides the clocks for the recov-
ery section and for the enable/disable timers. Card present goes low after 8 or
9 flux reversals are seen from the magnetic pickup and will return high about
50 ms after the last flux reversal. The strobe line signals that data is valid
and is active low. The data pin indicates a one bit when it is low. Raw F/2F
data can also be picked directly off the chip.
The data rate for a high-density track scanned at 50 ips comes to 10500 bits
per second (bps). This results in a transfer rate of 1500 characters per second
for the 7-bit elements used on track 1, and 2100 characters per second using
the 5-bit elements of track 3. I either case, this translates to a new bit
arriving at the controller just under every 100 us (microsecond). Even the most
anemic controller should be able to keep up. With resonably good coding techni-
ques, there should be no problem handling the entire data sampling phase on an
interrupt-driven basis. The low-density (track 2) data flows at a more pedes-
trian 3750 bps, yielding 750 5-bit characters per second, or a new bit every
266 us. Since most dual-track read heads provide track 1 and track 2 data, this
indicates that handling both tracks simultaneously is feasible under interrupt
control. Keep in mind that 50 ips is a rather fast scan rate; 20-30 ips is
probably a more realistic limit.
MAGNETIC BIT STORMS
When approaching a problem such as decoding magnetic cards, it pays to spend
some time looking at the overall picture before starting to write the code. At
first glance, it would seem that organizing the data into the prevailing element
size during the sampling interval would make decoding easier. This could be
easily done by ignoring all the leading zeros, with actual data storage comm-
encing with the first one bit. Of course, this approach assumes you're getting
good data. The fact that the data recovery is handled using well-proven hard-
ware makes this assumption valid.
If all you need to do is decode the card in a forward direction, then going
about things as I just described makes sense and reduces the coding effort to a
trivial exercise. If you have to support reverse decoding then this is not the
optimal solution. Having considered the tradeoffs of being able to decode a
magnetic card in both forward and reverse directions, I decided to structure the
program to work equally well in either direction at the cost of a slight
increase in initial complexity.
The first step in decoding is to acquire the serial bit stream. This can be
done using a dedicated sample loop or, with a little more work, using interrupt
processing. Since the idea is the same regardless of the details, I decided to
use a sample loop in my demonstration program (listing 1). The code simply
records the incoming data stream and deposits the data in a sample buffer a byte
at a time. Sampling begins when Card Present returns idle. Any incomplete byte
that has been partially assembled at the time when sampling terminates is simply
discarded. The abundance of leading and trailing zeros allows losing some bits
at either end causing any problems.
Once the sampling interval completes, control is transferred to the decoding
algorithm. Presented in listing 2, the track-1 decode algorithm consists of
nothing more than some initialization and the essence of the decode logic.
Limiting the gyrations contained in the main body of this routine not only makes
the logic easy to follow, but permits the same code to handle the decoding in
either a forward or reverse direction.
The initial entry point assumes a forward decode attempt and sets up the
necessary flags, pointers, and counters before jumping into the main initial-
ization code. After initialization, the sample buffer is scanned for the first
one bit, at which time a 7-bit element is assembled. If the parity is correct
and the character code checks out to be a Start Sentinel, the code proceeds and
starts pulling successive data elements from the sample buffer. If the data
element is not an End Sentinel, the character is translated to ASCII and stored
in the decode buffer. Should an End Sentinel be detected, the program extracts
the next character, which is assumed to be the LRC byte, and finally checks the
calculated LRC for a value of zero.
The checks and balances included in the execution of this loop include things
such as parity, a cumulative LRC, and checking to make sure I haven't run out of
samples. If everything checks out, the program terminates and returns with the
DPTR pointing to the decoded data buffer and the character count contained in
ACC. Should a decode failure occur, a test is performed on the direction flag
and if this is an attempt at a forward decode, the routine jumps to the reverse
initialization entry point. The reverse entry is similar to the forward decode
entry but sets up the sample pointer to the end of the sample buffer and sets
the direction flag to indicate a reverse operation.
The routines contained in the intermediate layer are shown in listing 3. The
meaning and operation of these routines should be apparent. The key routine in
this section is GET_BIT, which picks off the next bit from the sample buffer,
essentially restoring the sequential nature of the initial magnetic bit stream.
FIND_START is used to synchronize with the first one bit. GET_CHAR first checks
to make sure it hasn't run out of samples, then assembles the next 7-bit data
element while doing a parity test and LRC calculation. Any problems encountered
here are sent back to the caller and are handled there. STORE_CHAR translates
and deposits the data character into its respective location in the decoded-data
buffer and increments the character counter.
Listing 4 shows the low-level code. These routines perform the most rudiment-
ary functions and operate in accordance with the direction flag. INDEX_PTR
either increments or decrements the sample pointer, POSITION_BIT likewise does
either a right or left shift and LOCATE_BIT returns the state of the least- or
most- significant bit of the accumulator.
GO AHEAD, TAKE A SWIPE
Let me touch on a few additional points that may not be immediately apparent
before signing off. Storing the sampled data in a continuous stream makes the
sample routine work equally well with the various bit configurations used for
the different recording tracks. This would not be easily attained if you tried
to generate a particular element format during sample time. Furthermore, if you
look at the differences between the encoded character sets and the bit formats
for the different tracks, you will find that they differ in only a few areas.
With a few minor changes, such as the defined Start Sentinel, number of bits per
element, and character translation method, the decode routine I've shown could
easily be coerced to handle the decoding of any of the standard magnetic tracks.
As a matter of fact, by recoding and redefining the hard-coded constants as
variables, these could be set up for the particular data track at execution
time before invoking the decode function. Doing so would not only save program
memory, but would also allow you to use a routine you were comfortable with.
*******************************************************************************
FIGURE 1
_____________________________________________________________________
TRACK 1 |SS|FC| PAN |FS| NAME |FS| ADDITIONAL DATA |ES|LRC|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Notes: Track 1 is limited to 79 characters including SS, ES, and LRC.
Mastercard PAN is variable up to 16 characters maximum. VISA is 13 or 16
characters, including mod-10 check digit.
SS: Start sentinel (%)
FC: Format code
FS: Field separator ({)
ES: End sentinel (?)
LRC: Longitudinal redundency check character
PAN (primary account number): 19 digits max.
NAME: 26 alphanumeric characters max.
ADDITIONAL DATA: Expiration date 4
Restriction or type 3
Offset or PVN 5
______________________________________________________________________
TRACK 2 |SS|FC| PAN |FS| ADDITIONAL DATA |ES|LRC|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SS: Start sentinel (;) (hex B)
FS: Field separator (=) (hex D)
ES: End sentinel (?) (hex F)
LRC: Longitudinal redundency check character
PAN (primary account number): 19 digits max.
ADDITIONAL DATA: Expiration date 4
Restriction or type 3
Offset or PVN 5
*****************************************************************************
FIGURE 2
HEAD SIGNAL __/~\__ __/~\__ __/~\__ __/~\__ __/~\__ __/~\_______
`-` `-` `-` `-` `-`
____ _______ __________ ____
CARD PRESENT |______________________________________________|
____ ____ _____________________ ____ ____ _____
READ DATA |____| |_________| |_________|
____ ______ __________ __ __ __ __ __ __ __ __ __ __
READ STROBE |__| |_| |_| |_| |_| |_| |_| |_| |_| |_| |
| 0| 1| 0| 1| 1| 0| 1| 1| 0| 0|
___
HEAD 1-----X---X--------13 |MAG| 9--C2-R3
R1 C1 |TEK| |
HEAD 2-----X---X--------12 | | 10-----X--X
| | | |
X---X------11 | | | R5
X-X R2 C6 | | 6------|--X
| | X---X-------8 | | |
+5VDC --------------X--R7--X--------X-|-----------------14 | | 7-----C3
| |+ | | | ____
R6 C5 | | | 16----DATA
| X----------|------------------5 | | ______
____ _______ | | X------------------2 | | 15----STROBE
CARD PRESENT -------X------|-----------------------------1 | |
| X----X-----3 | |
| C4 R4----4 | |
GND------------------------X------------------X |___|
R=RESISTOR(Values weren't given)
C=CAPACITOR(Values weren't given)
X=CONNECTION BETWEEN WIRES
MAG TEK is the Mag-Tek 21006505
*****************************************************************************
LISTING 1-- Using several externally defined routines, a sample program to
read a stripe and store it in a buffer is very short.
PUBLIC READ_MAG1
EXTERN MS1_BUF (XDATA) ;sample buffer
EXTERN MS1_LIM (NUMBER) ;sample limit
EXTERN MD1_BUF (XDATA) ;decode buffer
EXTERN CP (BIT) ;card present bit
EXTERN M1_CLK (BIT) ;clock bit
EXTERN M1_DQ (BIT) ;data bit
M1_SS EQU 5 ;start sentinel
M1_ES EQU 1FH ;end sentinel
;
SEG CODE
;Sample and decode magnetic track 1
; output: ACC contains character count.
; DPTR points to data buffer
READ_MAG1 PROC
CALL MAG_SAMPLE
JZ L?RM1
CALL MAG1_DECODE
L?RM1: RET
ENDPROC
;General-purpose magnetic sampling routine
; output: ACC contains sample count
MAG_SAMPLE PROC
MOV DPTR,#MS1_BUF
MOV R1,#0 ;sample counter
L?MS1: MOV R0,#8 ;bit counter
L?MS2: JB CP,L?MS4
JB M1_CLK,L?MS2
MOV C,M1_DQ
L?MS3: JB CP,L?MS4
JNB M1_CLK,L?MS3
CPL C
RRC A
DJNZ R0,L?MS2
MOVX @DPTR,A
INC DPTR
INC R1 ;sample counter
CJNE R1,#MS1_LIM,L?MS1
L?MS4: MOV A,R1 ;final sample count
RET
ENDPROC
*******************************************************************************
LISTING 2-- Once the serial bit stream has been acquired, the decoding
algorithm takes over.
;Bidirectional magnetic track 1 decode routine
;input: sample count in ACC, output: ACC contains character count
; DPTR points to decoded data buffer
;Reg. usage for this routine (includes subroutines) as follows:
;R5: Direction flag, 0=forward
;R4: Cumulative LRC register
;R3: Decoded character counter
;R2: Nondecrementing sample count
;R1: Decrementing sample count
;R0: Bit syncronizing counter
MAG1_DECODE PROC
;1st pass, setup for forward decode attempt
MOV R5,#0 ;indicate forward decode
MOV DPTR,#MS1_BUF ;point to start of buffer
MOV R1,A ;sample counter
MOV R2,A ;sample count
JMP L?M1D1
L?M1D0: ;2nd pass, setup for reverse decode attempt
MOV R5,#1 ;indicate reverse decode
MOV DPTR,#MS1_BUF
MOV A,R2 ;sample count
DEC A
ADD A,DPL
MOV DPL,A
CLR A
ADDC A,DPH
MOV DPH,A ;point to end of buffer
MOV R1,2 ;sample counter
L?M1D1: ;decode initialization
MOV R3,#0 ;character counter
MOV R4,#0 ;inital LRC
MOV R0,#0 ;bit syncronizer
CALL FIND_START ;main decode loop
JNC L?M1D5 ;start bit error
CALL GET_CHAR ;Start Sentinel
JB ACC.7,L?M1D5 ;format error
CJNE A,#M1_SS,L?M1D5 ;start setinel error
L?M1D2: ;data byte or End Sentinel
CALL GET_CHAR
JB ACC.7,L?M1D5 ;format error
CJNE A,#M1_ES,L?M1D3 ;end sentinel not found
JMP L?M1D4
L?M1D3:
CALL STORE_CHAR ;data character
JMP L?M1D2
L?M1D4: ;LRC
CALL GET_CHAR ;get LRC
JB ACC.7,L?M1D5 ;format error
MOV A,R4
JNZ L?M1D5 ;LRC error
MOV DPTR,#MD1_BUF ;good return
MOV A,R3 ;final character
RET
L?M1D5: ;decode error, check if 1st pass
CJNE R5,#1,L?M1D0 ;check direction
CLR A ;bad return
RET
ENDPROC
*******************************************************************************
LISTING 3-- The intermediate layer of software is one level removed from the
nitty-gritty details.
;Get the next bit from the sample buffer
;output: C contains data bit
GET_BIT PROC
CJNE R0,#0,L?GB1 ;bit synchronizer
MOV R0,#8
PUSH ACC
MOVX A,@DPTR
CALL INDEX_PTR
MOV B,A
POP ACC
DEC R1 ;sample counter
L?GB1: XCH A,B
CALL POSITION_BIT
XCH A,B
DEC R0 ;bit synchronizer
RET
ENDPROC
;
;Find the first '1' bit in the sample buffer
;output: C=1 if bit is found
FIND_START PROC
L?FS1:
CJNE R0,#0,L?FS2 ;bit synchronizer
MOV R0,#8
MOVX A,@DPTR
CALL INDEX_PTR
DJNZ R1,L?FS2 ;sample counter
JMP L?FS4 ;out of samples
L?FS2: CALL LOCATE_BIT ;test for a '1' bit
JC L?FS3
CALL POSITION_BIT
DEC R0 ;bit synchronizer
JMP L?FS1
L?FS3: ;good return
MOV B,A ;save copy in B
SETB C
RET
L?FS4: CLR C ;bad return
RET
ENDPROC
;
;Get the next 7 bit element from the sample buffer
;output: ACC contains data element
; error flag is ACC.7
GET_CHAR PROC
MOV A,R1 ;sample counter
JZ L?GC2 ;out of samples
MOV R7,#7 ;bit counter
CLR A
L?GC1: CALL GET_BIT ;next bit
RRC A
DJNZ R7,L?GC1
RR A
JNB P,L?GC2 ;parity error
ANL A,#3FH ;discard parity
PUSH ACC
XRL A,R4 ;calculate LRC
MOV R4,A
POP ACC ;good return
RET
L?GC2: SETB ACC.7 ;bad return
RET
ENDPROC
;Translate and store the data character
;input: ACC contains data character
STORE_CHAR PROC
PUSH DPL
PUSH DPH
PUSH ACC
MOV DPTR,#MD1_BUF
MOV A,R3 ;character counter
ADD A,DPL
MOV DPL,A
CLR A
ADDC A,DPH ;generate displacement
MOV DPH,A
POP ACC
ADD A,#' ' ;translate
MOVX @DPTR,A ;store
POP DPH
POP DPL
INC R3 ;character counter
RET
ENDPROC
*******************************************************************************
LISTING 4-- The low-level routines get right down to the ground and take care
of the gory details.
;Index the sample pointer either forward or backward
INDEX_PTR PROC
CJNE R5,#0,L?IP1 ;check direction
INC DPTR ;forward
RET
L?IP1: PUSH ACC ;backward
DEC DPL
MOV A,DPL
CJNE A,#-1,L?IP2
DEC DPH
L?IP2: POP ACC
RET
ENDPROC
;Position bit is in ACC into C in either a right or left shift
POSITION_BIT PROC
CJNE R5,#0,L?PB1 ;check direction
RRC A ;forward
RET
L?PB1: RLC A
RET
ENDPROC
;Locate a 1 bit, either msb or lsb
;output: C=1 if bit is a one
LOCATE_BIT PROC
CJNE R5,#0,L?LB1 ;check direction
MOV C,ACC.0 ;forward
RET
L?LB1: MOV C,ACC.7 ;backward
RET
ENDPROC
*******************************************************************************
Contact:
Mag-Tek, Inc.
20725 S. Annalee Ave.
Carson, CA 90746
(213) 631-8602
fax: (213) 631-3956
*******************************************************************************
--
_
__ | __ | ` __ __ clafave@holonet.net
| | __| ~|~ __|| ||__| Beaverton, Oregon USA
|__ |_ |__| | |__| \/ |__. GO BLAZERS!
From clafave@iat.holonet.net (Christopher R LaFave)
Newsgroups: alt.2600
Subject: Magnetic stripe technology (2/2)
Date: Sat, 21 May 1994 06:23:54 GMT
>From PHRACK issue#37
*******************************************************************************
* *
* Card-O-Rama: Magnetic Stripe Technology and Beyond *
* *
* or *
* *
* "A Day in the Life of a Flux Reversal" *
* *
* *
* *
* by: ..oooOO Count Zero OOooo.. .RDT. 11/22/91 *
* *
*******************************************************************************
---A production of : -=Restricted -=Data -=Transmissions :
: :
: "Truth is cheap, but information costs." :
Look in your wallet. Chances are you own at least 3 cards that have
magnetic stripes on the back. ATM cards, credit cards, calling cards,
frequent flyer cards, ID cards, passcards,...cards, cards, cards! And chances
are you have NO idea what information is on those stripes or how they are
encoded. This detailed document will enlighten you and hopefully spark your
interest in this fascinating field. None of this info is 'illegal'...but
MANY organizations (government, credit card companies, security firms,
etc.) would rather keep you in the dark. Also, many people will IMMEDIATELY
assume that you are a CRIMINAL if you merely "mention" that you are
"interested in how magnetic stripe cards work." Watch yourself, ok? Just
remember that there's nothing wrong with wanting to know how things work, altho
in our present society, you may be labelled a "deviant" (or worse, a <gasp>
"hacker!").
Anyway, I will explain in detail how magstripes are encoded and give
several examples of the data found on some common cards. I will also cover the
technical theory behind magnetic encoding, and discuss magnetic encoding
alternatives to magstripes (Wiegand, barium ferrite). Non-magnetic card
technology (bar code, infrared, etc.) will be described. Finally, there will
be an end discussion on security systems and the ramifications of emergent
"smartcard" and biometric technologies.
*DISCLAIMER*
Use this info to EXPLORE, not to EXPLOIT. This text is presented for
informational purposes only, and I cannot be held responsible for anything you
do or any consequences thereof. I do not condone fraud, larceny, or any other
criminal activities.
*A WARNING*
I've noticed lately a few "books" and "magazines" for sale that were
FILLED with PHILES on a variety of computer topics. These philes were
originally released into the Net with the intention of distributing them for
FREE. HOWEVER, these philes are now being PACKAGED and sold FOR PROFIT. This
really pisses me off. I am writing this to be SHARED for FREE, and I ask no
payment. Feel free to reprint this in hardcopy format and sell it if you must,
but NO PROFITS must be made. Not a fucking DIME! If ANYONE reprints this
phile and tries to sell it FOR A PROFIT, I will hunt you down and make your
life miserable. How? Use your imagination. The reality will be worse.
** MAGSTRIPE FIELDS, HEADS, ENCODING/READING **
Whew! I'll get down to business now. First, I am going to explain the
basics behind fields, heads, encoding and reading. Try and absorb the THEORY
behind encoding/reading. This will help you greatly if you ever decide to
build your own encoder/reader from scratch (more on that later).
FERROMAGNETIC materials are substances that retain magnetism after an external
magnetizing field is removed. This principle is the basis of ALL magnetic
recording and playback. Magnetic POLES always occur in pairs within magnetized
material, and MAGNETIC FLUX lines emerge from the NORTH pole and
terminate at the SOUTH. The elemental parts of MAGSTRIPES are ferromagnetic
particles about 20 millionths of an inch long, each of which acts like a tiny
bar magnet. These particles are rigidly held together by a resin binder.
The magnetic particles are made by companies which make coloring pigments
for the paint industry, and are usually called pigments. When making the
magstripe media, the elemental magnetic particles are aligned with their
North-South axes parallel to the magnetic stripe by means of an external
magnetic fields while the binder hardens.
These particles are actually permanent bar magnets with TWO STABLE
POLARITIES. If a magnetic particle is placed in a strong external magnetic
field of the opposite polarity, it will FLIP its own polarity (North becomes
South, South becomes North). The external magnetic field strength required to
produce this flip is called the COERCIVE FORCE, or COERCIVITY of the particle.
Magnetic pigments are available in a variety of coercivities (more on that
lateron).
An unencoded magstripe is actually a series of North-South magnetic
domains (see Figure 1). The adjacent N-S fluxes merge, and the entire stripe
acts as a single bar magnet with North and South poles at its ends.
Figure 1: N-S.N-S.N-S.N-S.N-S.N-S.N-S.N-S <-particles in stripe
---------
represented as-> N-----------------------------S
However, if a S-S interface is created somewhere on the stripe, the fluxes
will REPEL, and we get a concentration of flux lines around the S-S interface.
(same with N-N interface) ENCODING consists of creating S-S and N-N
interfaces, and READING consists of (you guessed it) detecting 'em. The S-S
and N-N interfaces are called FLUX REVERSALS.
||| ||| <-flux lines
Figure 2: N------------N-N-S-S-----------------S
--------- flux lines -> ||| |||
The external magnetic field used to flip the polarities is produced by a
SOLENOID, which can REVERSE its polarity by reversing the direction of CURRENT.
An ENCODING head solenoid looks like a bar magnet bent into the shape of a ring
so that the North/South poles are very close and face each other across a tiny
gap. The field of the solenoid is concentrated across this gap, and when
elemental magnetic particles of the magstripe are exposed to this field, they
polarize to the OPPOSITE (unlike poles attract). Movement of the stripe past
the solenoid gap during which the polarity of the solenoid is REVERSED will
produce a SINGLE flux reversal (see Figure 3). To erase a magstripe, the
encoding head is held at a CONSTANT polarity and the ENTIRE stripe is moved
past it. No flux reversals, no data.
| | <----wires leading to solenoid
| | (wrapped around ring)
/-|-|-\
/ \
Figure 3: | | <----solenoid (has JUST changed polarity)
--------- \ /
\ N S / <---gap in ring.. NS polarity across gap
N----------------------SS-N-------------------------S
^^
<<<<<-direction of stripe movement
S-S flux reversal created at trailing edge of solenoid!
So, we now know that flux reversals are only created the INSTANT the
solenoid CHANGES its POLARITY. If the solenoid in Figure 3 were to remain at
its current polarity, no further flux reversals would be created as the
magstripe moves from right to left. But, if we were to change the solenoid
gap polarity from NS to *SN*, then (you guessed it) a *N-N* flux reversal would
instantly be created. Just remember, for each and every reversal in solenoid
polarity, a single flux reversal is created (commit it to memory..impress your
friends..be a tech weenie!). An encoded magstripe is therefore just a series
of flux reversals (NN followed by SS followed by NN ...).
DATA! DATA! DATA! That's what you want! How the hell are flux reversals
read and interpreted as data? Another solenoid called a READ HEAD is used to
detect these flux reversals. The read head operates on the principle of
ELECTROMAGNETIC RECIPROCITY: current passing thru a solenoid produces a
magnetic field at the gap, therefore, the presence of a magnetic field at the
gap of a solenoid coil will *produce a current in the coil*! The strongest
magnetic fields on a magstrip are at the points of flux reversals. These are
detected as voltage peaks by the reader, with +/- voltages corresponding to
NN/SS flux reversals (remember, flux reversals come in 2 flavors).
See Figure 4.
magstripe---> -------NN--------SS--------NN---------SS------
Figure 4: voltage-----> .......+.........-.........+...........-.....
---------
---------- -------------
peak readout--> | | | |
--------| |----------| |----
The 'peak readout' square waveform is critical. Notice that the voltage
peak remains the same until a new flux reversal is encountered.
Now, how can we encode DATA? The most common technique used is known as
Aiken Biphase, or 'two-frequency coherent-phase encoding' (sounds impressive,
eh?). First, digest the diagrams in Figure 5.
Figure 5: ---------- ---------- ----------
--------- | | | | | | <- peak
a) | |--------| |--------| | readouts
* 0 * 0 * 0 * 0 * 0 *
----- ----- ----- ----- ----- -
| | | | | | | | | | |
b) | |----| |----| |----| |----| |----|
* 1 * 1 * 1 * 1 * 1 *
----- ---------- ----- ----- -
| | | | | | | | |
c) | |----| |--------| |----| |----|
* 1 * 0 * 0 * 1 * 1 *
There ya have it. Data is encoded in 'bit cells,' the frequency of which
is the frequency of '0' signals. '1' signals are exacty TWICE the frequency
of '0' signals. Therefore, while the actual frequency of the data passing
the read head will vary due to swipe speed, data density, etc, the '1'
frequency will ALWAYS be TWICE the '0' frequency. Figure 5C shows exactly how
'1' and '0' data exists side by side.
We're getting closer to read DATA! Now, we're all familiar with binary
and how numbers and letters can be represented in binary fashion very easily.
There are obviously an *infinite* number of possible standards, but thankfully
the American National Standards Institute (ANSI) and the International
Standards Organization (ISO) have chosen 2 standards. The first is
** ANSI/ISO BCD Data format **
This is a 5-bit Binary Coded Decimal format. It uses a 16-character set,
which uses 4 of the 5 available bits. The 5th bit is an ODD parity bit, which
means there must be an odd number of 1's in the 5-bit character..the parity bit
will 'force' the total to be odd. Also, the Least Significant Bits are read
FIRST on the strip. See Figure 6.
The sum of the 1's in each case is odd, thanks to the parity bit. If the
read system adds up the 5 bits and gets an EVEN number, it flags the read
as ERROR, and you gotta scan the card again. (yeah, I *know* a lot of you
out there *already* understand parity, but I gotta cover all the bases...not
everyone sleeps with their modem and can recite the entire AT command set
at will, you know ;). See Figure 6 for details of ANSI/ISO BCD.
Figure 6: ANSI/ISO BCD Data Format
---------
* Remember that b1 (bit #1) is the LSB (least significant bit)!
* The LSB is read FIRST!
* Hexadecimal conversions of the Data Bits are given in parenthesis (xH).
--Data Bits-- Parity
b1 b2 b3 b4 b5 Character Function
0 0 0 0 1 0 (0H) Data
1 0 0 0 0 1 (1H) "
0 1 0 0 0 2 (2H) "
1 1 0 0 1 3 (3H) "
0 0 1 0 0 4 (4H) "
1 0 1 0 1 5 (5H) "
0 1 1 0 1 6 (6H) "
1 1 1 0 0 7 (7H) "
0 0 0 1 0 8 (8H) "
1 0 0 1 1 9 (9H) "
0 1 0 1 1 : (AH) Control
1 1 0 1 0 ; (BH) Start Sentinel
0 0 1 1 1 < (CH) Control
1 0 1 1 0 = (DH) Field Separator
0 1 1 1 0 > (EH) Control
1 1 1 1 1 ? (FH) End Sentinel
***** 16 Character 5-bit Set *****
10 Numeric Data Characters
3 Framing/Field Characters
3 Control Characters
The magstripe begins with a string of Zero bit-cells to permit the
self-clocking feature of biphase to "sync" and begin decoding.
A "Start Sentinel" character then tells the reformatting process where to start
grouping the decoded bitstream into groups of 5 bits each. At the end of the
data, an "End Sentinel" is encountered, which is followed by an "Longitudinal
Redundancy Check (LRC) character. The LRC is a parity check for the sums of
all b1, b2, b3, and b4 data bits of all preceding characters. The LRC
character will catch the remote error that could occur if an individual
character had two compensating errors in its bit pattern (which would fool the
5th-bit parity check).
The START SENTINEL, END SENTINEL, and LRC are collectively called "Framing
Characters", and are discarded at the end of the reformatting process.
** ANSI/ISO ALPHA Data Format **
Alphanumeric data can also be encoded on magstripes. The second ANSI/ISO
data format is ALPHA (alphanumeric) and involves a 7-bit character set with
64 characters. As before, an odd parity bit is added to the required 6 data
bits for each of the 64 characters. See Figure 7.
Figure 7:
--------- ANSI/ISO ALPHA Data Format
* Remember that b1 (bit #1) is the LSB (least significant bit)!
* The LSB is read FIRST!
* Hexadecimal conversions of the Data Bits are given in parenthesis (xH).
------Data Bits------- Parity
b1 b2 b3 b4 b5 b6 b7 Character Function
0 0 0 0 0 0 1 space (0H) Special
1 0 0 0 0 0 0 ! (1H) "
0 1 0 0 0 0 0 " (2H) "
1 1 0 0 0 0 1 # (3H) "
0 0 1 0 0 0 0 $ (4H) "
1 0 1 0 0 0 1 % (5H) Start Sentinel
0 1 1 0 0 0 1 & (6H) Special
1 1 1 0 0 0 0 ' (7H) "
0 0 0 1 0 0 0 ( (8H) "
1 0 0 1 0 0 1 ) (9H) "
0 1 0 1 0 0 1 * (AH) "
1 1 0 1 0 0 0 + (BH) "
0 0 1 1 0 0 1 , (CH) "
1 0 1 1 0 0 0 - (DH) "
0 1 1 1 0 0 0 . (EH) "
1 1 1 1 0 0 1 / (FH) "
0 0 0 0 1 0 0 0 (10H) Data (numeric)
1 0 0 0 1 0 1 1 (11H) "
0 1 0 0 1 0 1 2 (12H) "
1 1 0 0 1 0 0 3 (13H) "
0 0 1 0 1 0 1 4 (14H) "
1 0 1 0 1 0 0 5 (15H) "
0 1 1 0 1 0 0 6 (16H) "
1 1 1 0 1 0 1 7 (17H) "
0 0 0 1 1 0 1 8 (18H) "
1 0 0 1 1 0 0 9 (19H) "
0 1 0 1 1 0 0 : (1AH) Special
1 1 0 1 1 0 1 ; (1BH) "
0 0 1 1 1 0 0 < (1CH) "
1 0 1 1 1 0 1 = (1DH) "
0 1 1 1 1 0 1 > (1EH) "
1 1 1 1 1 0 0 ? (1FH) End Sentinel
0 0 0 0 0 1 0 @ (20H) Special
1 0 0 0 0 1 1 A (21H) Data (alpha)
0 1 0 0 0 1 1 B (22H) "
1 1 0 0 0 1 0 C (23H) "
0 0 1 0 0 1 1 D (24H) "
1 0 1 0 0 1 0 E (25H) "
0 1 1 0 0 1 0 F (26H) "
1 1 1 0 0 1 1 G (27H) "
0 0 0 1 0 1 1 H (28H) "
1 0 0 1 0 1 0 I (29H) "
0 1 0 1 0 1 0 J (2AH) "
1 1 0 1 0 1 1 K (2BH) "
0 0 1 1 0 1 0 L (2CH) "
1 0 1 1 0 1 1 M (2DH) "
0 1 1 1 0 1 1 N (2EH) "
1 1 1 1 0 1 0 O (2FH) "
0 0 0 0 1 1 1 P (30H) "
1 0 0 0 1 1 0 Q (31H) "
0 1 0 0 1 1 0 R (32H) "
1 1 0 0 1 1 1 S (33H) "
0 0 1 0 1 1 0 T (34H) "
1 0 1 0 1 1 1 U (35H) "
0 1 1 0 1 1 1 V (36H) "
1 1 1 0 1 1 0 W (37H) "
0 0 0 1 1 1 0 X (38H) "
1 0 0 1 1 1 1 Y (39H) "
0 1 0 1 1 1 1 Z (3AH) "
1 1 0 1 1 1 0 [ (3BH) Special
0 0 1 1 1 1 1 \ (3DH) Special
1 0 1 1 1 1 0 ] (3EH) Special
0 1 1 1 1 1 0 ^ (3FH) Field Separator
1 1 1 1 1 1 1 _ (40H) Special
***** 64 Character 7-bit Set *****
* 43 Alphanumeric Data Characters
* 3 Framing/Field Characters
* 18 Control/Special Characters
The two ANSI/ISO formats, ALPHA and BCD, allow a great variety of data to be
stored on magstripes. Most cards with magstripes use these formats, but
occasionally some do not. More about those lateron.
** Tracks and Encoding Protocols **
Now we know how the data is stored. But WHERE is the data stored on the
magstripe? ANSI/ISO standards define *3* Tracks, each of which is used for
different purposes. These Tracks are defined only by their location on the
magstripe, since the magstripe as a whole is magnetically homogeneous. See
Figure 8.
Figure 8:
--------- <edge of card>
_________________________________________________________________
| ^ ^ ^
|------------------| 0.223"--|---------|-------------------------
| | | 0.353" | ^
|..................|.........|.........| 0.493" |
| Track #1 0.110" | | |
|............................|.........|... <MAGSTRIPE>
| | | |
|............................|.........|... |
| Track #2 0.110" | |
|......................................|... |
| | |
|......................................|... |
| Track #3 0.110" |
|.......................................... |
| |
|------------------------------------------------------------------
|
| <body of card>
|
You can see the exact distances of each track from the edge of the card, as
well as the uniform width and spacing. Place a magstripe card in front of you
with the magstripe visible at the bottom of the card. Data is encoded from
left to right (just like reading a book, eh?). See Figure 9.
Figure 9:
--------- ANSI/ISO Track 1,2,3 Standards
Track Name Density Format Characters Function
--------------------------------------------------------------------
1 IATA 210 bpi ALPHA 79 Read Name & Account
2 ABA 75 bpi BCD 40 Read Account
3 THRIFT 210 bpi BCD 107 Read Account &
*Encode* Transaction
*** Track 1 Layout: ***
| SS | FC | PAN | Name | FS | Additional Data | ES | LRC |
SS=Start Sentinel "%"
FC=Format Code
PAN=Primary Acct. # (19 digits max)
FS=Field Separator "^"
Name=26 alphanumeric characters max.
Additional Data=Expiration Date, offset, encrypted PIN, etc.
ES=End Sentinel "?"
LRC=Longitudinal Redundancy Check
*** Track 2 Layout: ***
| SS | PAN | FS | Additional Data | ES | LRC |
SS=Start Sentinel ";"
PAN=Primary Acct. # (19 digits max)
FS=Field Separator "="
Additional Data=Expiration Date, offset, encrypted PIN, etc.
ES=End Sentinel "?"
LRC=Longitudinal Redundancy Check
*** Track 3 Layout: ** Similar to tracks 1 and 2. Almost never used.
Many different data standards used.
Track 2, "American Banking Association," (ABA) is most commonly used. This
is the track that is read by ATMs and credit card checkers. The ABA designed
the specifications of this track and all world banks must abide by it. It
contains the cardholder's account, encrypted PIN, plus other discretionary
data.
Track 1, named after the "International Air Transport Association," contains
the cardholder's name as well as account and other discretionary data. This
track is sometimes used by the airlines when securing reservations with a
credit card; your name just "pops up" on their machine when they swipe your
card!
Since Track 1 can store MUCH more information, credit card companies are trying
to urge retailers to buy card readers that read Track 1. The *problem* is that
most card readers read either Track 1 or Track 2, but NOT BOTH! And the
installed base of readers currently is biased towards Track 2. VISA USA is at
the front of this 'exodus' to Track 1, to the point where they are offering
Track 1 readers at reduced prices thru participating banks. A spokesperson for
VISA commented:
"We think that Track 1 represents more flexibility and the
potential to deliver more information, and we intend to
build new services around the increased information."
What new services? We can only wait and see.
Track 3 is unique. It was intended to have data read and WRITTEN on it.
Cardholders would have account information UPDATED right on the magstripe.
Unfortunately, Track 3 is pretty much an orphaned standard. Its *original*
design was to control off-line ATM transactions, but since ATMs are now on-line
ALL THE TIME, it's pretty much useless. Plus the fact that retailers and banks
would have to install NEW card readers to read that track, and that costs $$.
Encoding protocol specifies that each track must begin and end with a length
of all Zero bits, called CLOCKING BITS. These are used to synch the self-
clocking feature of biphase decoding. See Figure 10.
Figure 10: end sentinel
start sentinel | longitudinal redundancy check
| | |
000000000000000 SS.................ES LRC 0000000000000000
leading data, data, data trailing
clocking bits clocking bits
(length varies) (length varies)
THAT'S IT!!! There you have the ANSI/ISO STANDARDS! Completely explained.
Now, the bad news. NOT EVERY CARD USES IT! Credit cards and ATM cards will
follow these standards. BUT, there are many other types of cards out there.
Security passes, copy machine cards, ID badges, and EACH of them may use a
PROPRIETARY density/format/track-location system. ANSI/ISO is REQUIRED for
financial transaction cards used in the international interbank network. All
other cards can play their own game.
The good news. MOST other cards follow the standards, because it's EASY to
follow a standard instead of WORKING to make your OWN! Most magstripe cards
other than credit cards and ATM cards will use the same Track specifications,
and use either BCD or ALPHA formats.
** A Bit About Magstripe Equipment **
"Wow, now I know how to interpret all that data on magstripes! But...
waitasec, what kind of equipment do I need to read the stripes?
Where can I buy a reader? I don't see any in Radio Shack!!"
Sorry, but magstripe equipment is hard to come by. For obvious reasons,
card readers are not made commonly available to consumers. How to
build one is the topic for another phile (and THIS phile is already too long!).
Your best bets are to try and scope out Electronic Surplus Stores and flea
markets. Don't even bother trying to buy one directly from a manufacturer,
since they will immediately assume you have "criminal motives." And as for
getting your hands on a magstripe ENCODER...well, good luck! Those rare
beauties are worth their weight in gold. Keep your eyes open and look around,
and MAYBE you'll get lucky! A bit of social engineering can go a LONG way.
There are different kinds of magstripe readers/encoders. The most common
ones are "swipe" machines: the type you have to physically slide the card thru.
Others are "insertion" machines: like ATM machines they 'eat' your card, then
regurgitate it after the transaction. Costs are in the thousands of dollars,
but like I said, flea markets and surplus stores will often have GREAT deals
on these things. Another problem is documentation for these machines. If you
call the manufacturer and simply ask for 'em, they will probably deny you the
literature. "Hey son, what are you doing with our model XYZ swipe reader? That
belongs in the hands of a 'qualified' merchant or retailer, not some punk kid
trying to 'find out how things work!" Again, some social engineering may be
required. Tell 'em you're setting up a new business. Tell 'em you're working
on a science project. Tell 'em anything that works!
2600 Magazine recently had a good article on how to build a machine that
copies magstripe cards. Not much info on the actual data formats and encoding
schemes, but the device described is a start. With some modifications, I bet
you could route the output to a dumb terminal (or thru a null modem cable) in
order to READ the data. Worth checking out the schematics.
As for making your own cards, just paste a length of VCR, reel-to-reel, or
audio cassette tape to a cut-out posterboard or plastic card. Works just as
good as the real thing, and useful to experiment with if you have no expired or
'dead' ATM or calling cards lying around (SAVE them, don't TOSS them!).
** Examples of Data on Magstripes **
The real fun in experimenting with magstripe technology is READING cards to
find out WHAT THE HELL is ON them! Haven't you wondered? The following cards
are the result of my own 'research'. Data such as specific account numbers and
names has been changed to protect the innocent. None the cards used to make
this list were stolen or acquired illegally.
Notice that I make careful note of 'common data'; data that I noticed was
the same for all cards of a particular type. This is highlighted below the
data with asterisks (*). Where I found varying data, I indicate it with "x"'s.
In those cases, NUMBER of CHARACTERS was consistent (the number of "x"'s equals
the number of characters...one to one relationship).
I still don't know what some of the data fields are for, but hopefully I
will be following this phile with a sequel after I collect more data. It ISN'T
easy to find lots of cards to examine. Ask your friends, family, and co-workers
to help! "Hey, can I, um, like BORROW your MCI calling card tonite? I'm
working on an, um, EXPERIMENT. Please?" Just...be honest! Also, do some
trashing. People will often BEND expired cards in half, then throw them out.
Simply bend 'em back into their normal shape, and they'll usually work (I've
done it!). They may be expired, but they're not ERASED!
-------------------------------------------------------------------------------
-=Mastercard=- Number on front of card -> 1111 2222 3333 4444
Expiration date -> 12/99
Track 2 (BCD,75 bpi)-> ;1111222233334444=99121010000000000000?
***
Track 1 (ALPHA,210 bpi)-> %B1111222233334444^PUBLIC/JOHN?
*
Note that the "101" was common to all MC cards checked, as well as the "B".
-------------------------------------------------------------------------------
-=VISA=- Number on front of card -> 1111 2222 3333 4444
Expiration date -> 12/99
Track 2 (BCD,75 bpi)-> ;1111222233334444=9912101xxxxxxxxxxxxx?
***
Track 1 (ALPHA,210 bpi)-> %B1111222233334444^PUBLIC/JOHN^9912101xxxxxxxxxxxxx?
*
Note that the "101" was common to all VISA cards checked, as well as the "B".
Also, the "xxx" indicates numeric data that varied from card to card, with no
apparent pattern. I believe this is the encrypted pin for use when cardholders
get 'cash advances' from ATMs. In every case, tho, I found *13* digits of the
stuff.
-------------------------------------------------------------------------------
-=Discover=- Number on front of card -> 1111 2222 3333 4444
Expiration date -> 12/99
Track 2 (BCD,75 bpi)-> ;1111222233334444=991210100000?
********
Track 1 (ALPHA,210 bpi)-> %B1111222233334444^PUBLIC/JOHN___^991210100000?
********
Note, the "10100000" and "B" were common to most DISCOVER cards checked.
I found a few that had "10110000" instead. Don't know the significance.
Note the underscores after the name JOHN. I found consistently that the name
data field had *26* charaters. Whatever was left of the field after the name
was "padded" with SPACES. Soo...for all of you with names longer than 25
(exclude the "/") charaters, PREPARE to be TRUNCATED! ;)
-------------------------------------------------------------------------------
-=US Sprint FON=- Number on front of card -> 111 222 3333 4444
Track 2 (BCD,75 bpi)-> ;xxxxxx11122233339==xxx4444xxxxxxxxxx=?
*
Track 1 (ALPHA,210 bpi)-> %B^ /^^xxxxxxxxxxxxxxxxx?
*
Strange. None of the cards I check had names in the Track 1 fields. Track 1
looks unused, yet it was always formatted with field separators. The "xxx"
stuff varied from card to card, and I didn't see a pattern. I know it isn't
a PIN, so it must be account data.
-------------------------------------------------------------------------------
-=Fleet Bank=- Number on front of card -> 111111 222 3333333
Expiration date -> 12/99
Track 2 (BCD,75 bpi)-> ;1111112223333333=9912120100000000xxxx?
****
Track 1 (ALPHA,210 bpi) ->
%B1111112223333333^PUBLIC/JOHN___^9912120100000000000000xxxx000000?
* ****
Note that the "xxx" data varied. This is the encrypted PIN offset. Always 4
digits (hrmmm...). The "1201" was always the same. In fact, I tried many
ATM cards from DIFFERENT BANKS...and they all had "1201".
-------------------------------------------------------------------------------
(Can't leave *this* one out ;)
-=Radio Shack=- Number on front of card -> 1111 222 333333
NO EXPIRATION data on card
Track 2 (BCD,75 dpi)-> ;1111222333333=9912101?
*******
Note that the "9912101" was the SAME for EVERY Radio Shack card I saw. Looks
like when they don't have 'real' data to put in the expiration date field, they
have to stick SOMETHING in there.
-------------------------------------------------------------------------------
Well, that's all I'm going to put out right now. As you can see, the major
types of cards (ATMs, CC) all follow the same rules more or less. I checked
out a number of security passcards and timeclock entry cards..and they ALL had
random stuff written to Track 2. Track 2 is by FAR the MOST utilized track on
the card. And the format is pretty much always ANSI/ISO BCD. I *did* run
into some hotel room access cards that, when scanned, were GARBLED. They most
likely used a character set other than ASCII (if they were audio tones, my
reader would have put out NOTHING...as opposed to GARBLED data). As you can
see, one could write a BOOK listing different types of card data. I intended
only to give you some examples. My research has been limited, but I tried to
make logical conclusions based on the data I received.
** Cards of All Flavors **
People wanted to store A LOT of data on plastic cards. And they wanted that
data to be 'invisible' to cardholders. Here are the different card
technologies that were invented and are available today.
HOLLERITH - With this system, holes are punched in a plastic or paper card and
read optically. One of the earliest technologies, it is now seen
as an encoded room key in hotels. The technology is not secure,
but cards are cheap to make.
BAR CODE - The use of bar codes is limited. They are cheap, but there is
virtually no security and the bar code strip can be easily damaged.
INFRARED - Not in widespread use, cards are factory encoded by creating a
"shadow pattern" within the card. The card is passed thru a swipe
or insertion reader that uses an infrared scanner. Infrared card
pricing is moderate to expensive, and encoding is pretty secure.
Infrared scanners are optical and therefore vulnerable to
contamination.
PROXIMITY - Hands-free operation is the primary selling point of this card.
Altho several different circuit designs are used, all proximity
cards permit the transmission of a code simply by bringing the card
near the reader (6-12"). These cards are quite thick, up to
0.15" (the ABA standard is 0.030"!).
WIEGAND - Named after its inventor, this technology uses a series of small
diameter wires that, when subjected to a changing magnetic field,
induce a discrete voltage output in a sensing coil. Two rows of
wires are embedded in a coded strip. When the wires move past
the read head, a series of pulses is read and interpreted as binary
code. This technology prodces card that are VERY hard to copy
or alter, and cards are moderately expensive to make. Readers
based on this tech are epoxy filled, making them immune to weather
conditions, and neither card nor readers are affected by external
magnetic fields (don't worry about leaving these cards on top of
the television set...you can't hurt them!). Here's an example of
the layout of the wires in a Wiegand strip:
||| || || | ||| | || || | || || | | ||
| | | | | | |||| || |||| ||
The wires are NOT visible from the outside of the card, but if
your card is white, place it in front of a VERY bright light source
and peer inside. Notice that the spacings between the wires is
uniform.
BARIUM FERRITE - The oldest magnetic encoding technology (been around for 40
yrs!) it uses small bits of magnetized barium ferrite that are
placed inside a plastic card. The polarity and location of
the "spots" determines the coding. These cards have a short
life cycle, and are used EXTENSIVELY in parking lots (high
turnover rate, minimal security). Barium Ferrite cards are
ONLY used with INSERTION readers.
There you have the most commonly used cards. Magstripes are common because
they are CHEAP and relatively secure.
** Magstripe Coercivity **
Magstripes themselves come in different flavors. The COERCIVITY of the
magnetic media must be specified. The coercivity is the magnetic field
strength required to demagnetize an encoded stripe, and therefore determines
the encode head field strength required to encode the stripe. A range of media
coerciviteis are available ranging from 300 Oersteds to 4,000 Oe. That boils
down to HIGH-ENERGY magstripes (4,000 Oe) and LOW-ENERGY magstripes (300 Oe).
REMEMBER: since all magstripes have the same magnetic remanence regardless of
their coercivity, readers CANNOT tell the difference between HIGH and LOW
energy stripes. Both are read the same by the same machines.
LOW-ENERGY media is most common. It is used on all financial cards, but its
disadvantage is that it is subject to accidental demagnetization from contact
with common magnets (refrigerator, TV magnetic fields, etc.). But these cards
are kept safe in wallets and purses most of the time.
HIGH-ENERGY meda is used for ID Badges and access control cards, which are
commonly used in 'hostile' environments (worn on uniform, used in stockrooms).
Normal magnets will not affect these cards, and low-energy encoders cannot
write to them.
** Not All that Fluxes is Digital **
Not all magstripe cards operate on a digital encoding method. SOME cards
encode AUDIO TONES, as opposed to digital data. These cards are usually
used with old, outdated, industrial-strength equipment where security is not an
issue and not a great deal of data need be encoded on the card. Some subway
passes are like this. They require only expiration data on the magstripe, and
a short series of varying frequencies and durations are enough. Frequencies
will vary with the speed of swiping, but RELATIVE frequencies will remain the
same (for instance, tone 1 is twice the freq. of tone 2, and .5 the freq of
tone 3, regardless of the original frequencies!). Grab an oscilliscope to
visualize the tones, and listen to them on your stereo. I haven't experimented
with these types of cards at all.
** Security and Smartcards **
Many security systems utilize magstripe cards, in the form of passcards and
ID cards. It's interesting, but I found in a NUMBER of cases that there was
a serious FLAW in the security of the system. In these cases, there was a
code number PRINTED on the card. When scanned, I found this number encoded on
the magstripe. Problem was, the CODE NUMBER was ALL I found on the magstripe!
Meaning, by just looking at the face of the card, I immediately knew exactly
what was encoded on it. Ooops! Makes it pretty damn easy to just glance at
Joe's card during lunch, then go home and pop out my OWN copy of Joe's access
card! Fortunately, I found this flaw only in 'smaller' companies (sometimes
even universities). Bigger companies seem to know better, and DON'T print
ALL of the magstripe data right on card in big, easily legible numbers. At
least the big companies *I* checked. ;)
Other security blunders include passcard magstripes encoded ONLY with the
owner's social security number (yeah, real difficult to find out a person's
SS#...GREAT idea), and having passcards with only 3 or 4 digit codes.
Smartcard technology involves the use of chips embedded in plastic cards,
with pinouts that temporarily contact the card reader equipment. Obviously,
a GREAT deal of data could be stored in this way, and unauthorized duplication
would be very difficuly. Interestingly enough, not much effort is being put
into smartcards by the major credit card companies. They feel that the tech
is too expensive, and that still more data can be squeezed onto magstripe
cards in the future (especially Track 1). I find this somewhat analagous to
the use of metallic oxide disk media. Sure, it's not the greatest (compared
to erasable-writable optical disks), but it's CHEAP..and we just keep improving
it. Magstripes will be around for a long time to come. The media will be
refined, and data density increased. But for conventional applications, the
vast storage capabilities of smartcards are just not needed.
** Biometrics: Throw yer cards away! **
I'd like to end with a mention of biometrics: the technology based on reading
the physical attributes of an individual thru retina scanning, signature
verification, voice verification, and other means. This was once limited to
government use and to supersensitive installations. However, biometrics will
soon acquire a larger market share in access control sales because much of its
development stage has passed and costs will be within reach of more buyers.
Eventually, we can expect biometrics to replace pretty much ALL cards..because
all those plastic cards in your wallet are there JUST to help COMPANIES
*identify* YOU. And with biometrics, they'll know you without having to read
cards. I'm not paranoid, nor do I subscribe to any grand 'corporate
conspiracy', but I find it a bit unsettling that our physical attributes will
most likely someday be sitting in the cool, vast electronic databases of
the CORPORATE world. Accessable by anyone willing to pay. Imagine CBI and TRW
databases with your retina image, fingerprint, and voice pattern online for
instant, convenient retrieval. Today, a person can CHOOSE NOT to own a credit
card or a bank card...we can cut up our plastic ID cards! Without a card, a
card reader is useless and cannot identify you. Paying in cash makes you
invisible! However, with biometrics, all a machine has to do is watch...
.listen...and record. With government/corporate America pushing all the
buttons.. "Are you paying in cash?...thank you...please look into the camera.
Oh, I see your name is Mr. Smith...uh, oh...my computer tells me you haven't
paid your gas bill....afraid I'm going to have to keep this money and credit
your gas account with it....do you have any more cash?...or would you rather
I garnish your paycheck?" heh heh
** Closing Notes (FINALLY!!!!) **
Whew...this was one MOTHER of a phile. I hope it was interesting, and I hope
you distribute it to all you friends. This phile was a production of
"Restricted Data Transmissions"...a group of techies based in the Boston area
that feel that "Information is Power"...and we intend to release a number of
highly technical yet entertaining philes in the coming year....LOOK FOR THEM!!
Tomorrow I'm on my way to Xmascon '91.....we made some slick buttons
commemorating the event...if you ever see one of them (green wreath..XMASCON
1991 printed on it)..hang on to it!...it's a collector's item.. (hahahah)
Boy, I'm sleepy...
Remember.... "Truth is cheap, but information costs!"
But -=RDT is gonna change all that... ;) set the info FREE!
Peace.
..oooOO Count Zero OOooo..
count0@world.std.com
count0@spica.bu.edu
count0@atdt.org
ATDT------(???)YOU-WISH
(You're not paranoid if they're REALLY out to get you... ;)
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--
_
__ | __ | ` __ __ clafave@holonet.net
| | __| ~|~ __|| ||__| Beaverton, Oregon USA
|__ |_ |__| | |__| \/ |__. GO BLAZERS!

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